Vapor generator tube arrangement

ABSTRACT

A forced flow vapor generator wherein at least one of the upright boundary walls of the furnace has a lower and upper section formed of a first and second group of parallel flow tubes respectively, the tubes in each group being rigidly united throughout most of their lengths and having portions thereof interlaced and coextensive with each other, the interlaced portions being detached from one another for the most part. Provisions for interconnecting the tubes of the first and second groups including having inlet and outlet portions of the tubes bent out of the plane of the wall, the bent out portions being detached from one another for the most part.

United States Patent Barberton et al.

[541 VAPOR GENERATOR TUBE ARRANGEMENT [72] inventors: Carl Lleb Barberton; Murray Wiener,

both of Akron, Ohio [73] Assignee: The Babeoclt 8: Wilcox Company, New

York, NY.

[221 Filed: Dec. 29, 1970 [21] Appl.No.: 102,346

[56] References Cited UNITED STATES PATENTS 3,237,612 3/1966 Koch etal 122/406 S 51 May 30, 1972 Primary Examiner-Kenneth W. Sprague Attorney-J. Maguire [57] ABSTRACT A forced flow vapor generator wherein at least one of the upright boundary walls of the furnace has a lower and upper section formed of a first and second group of parallel flow tubes respectively, the tubes in each group being rigidly united throughout most of their lengths and having portions thereof interlaced and coextensive with each other, the interlaced portions being detached from one another for the most part. Provisions for interconnecting the tubes of the first and second groups including having inlet and outlet portions of the tubes bent out of the plane of the wall, the bent out portions being detached from one another for the most part.

14 Claims, 16 Drawing Figures Patented May 30, 1972 3,665,893

5 Sheets-Sheet l INVENTQRS Carl L |eb BY Murray WIener AT OR'NEY Patented May 30, 1972 5 Sheets-Sheet 2 Pa'tefited May 30, 1972 3,665,893

5 Sheets-Sheet 5 Patented May 30, 1972 5 Sheets-Sheet FIG.6C

BACKGROUND OF THE INVENTION This invention relates generally to the construction of a forced flow fluid heating unit, and more particularly to improvements in the construction and arrangement of the furnace fluid heating circuits of a forced circulation oncethrough steam generating and superheating unit.

The present invention is directed to improvements in the furnace fluid heating circuitry of a forced flow vapor generator of the type disclosed in US. application Ser. No. 447,699 wherein the upright boundary walls of the furnace are subdivided into a plurality of separate continuous upflow fluid heating passes with the parallel flow tubes of one of the fluid heating passes being interlaced and coextensive with the parallel flow tubes of another of the heating passes, and with special provisions for supporting and interconnecting the tubes of the fluid heating passes to provide a serial flow of fluid successively through the respective fluid passes to equalize fluid enthalpies as they flow from one furnace heating pass to another.

In furnace walls of prior units of the character described, portions of tubes of the separate heating passes form a common plane wherein they are interlaced and coextensive, and above and below this common plane, the tubes are bent outwardly of the plane of the wall and connected to suitably arranged headers. Laterally adjacent tubes are rigidly united to one another by metallic webs above and below the interlaced area and the point at which the tubes are bent outwardly from the plane of the wall. The intertube spacing at the point where the tubes leave the plane of the wall and at the interlaced and coextensive portions has been closed by seal plates welded to laterally adjacent tubes, however, due to the expansion and contraction of the wall during the heating and cooling of the unit, excessive stresses are created by these seal plates frequently resulting in cracking of the plates or tubes.

SUMMARY OF THE INVENTION In accordance with the present invention, the forced circulation fluid heating unit comprises upright walls forming a furnace for heating gases, with at least one of the walls including a first group of upwardly extending laterally spaced fluid heating tubes rigidly united by metallic webs throughout most of their length to for a lower portion of the wall, and a second group of upwardly extending laterally spaced fluid heating tubes rigidly united by metallic webs throughout most of their lengths to form an upper portionof the wall. Headers are provided for receiving and mixing fluid flowing from the tubes of the first group and distributing the fluids to the tubes of the second group. Some of the tubes of the first and second tube groups are bent out of the plane of the wall at first and second levels, respectively, for connection to the headers and interlaced with and laterally spaced from each other in the plane of the wall between the first and second levels, with the first level being subjacent the second level, the remainder of the tubes of the first and second tube groups being bent out of the plane of the wall at about the second and first levels, respectively, for connection to the header means. An arrangement for supporting the wall including support lugs weld united only to the interlaced portions of the second group of tubes, means for transmitting the load of the first group of tubes to the support lugs, and means for top supporting the second group of tubes, the tube portions in the plane of the wall in the vicinity of the first and second levels and at the interlaced portions therebetween being detached from one another for the most part. An alternate arrangement with provisions for supporting the wall including support lugs weld united only to the second group of tubes and supported lugs weld united only to the first group of tubes, means for transmitting the load of the first group of tubes to the support lugs, and means for top supporting the second group of tubes, the tube portions in the plane of the wall in the vicinity of the interlaced portion therebetween being detached from one another for the most part.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional side elevation of a once-through forced flow steam generator embodying the invention;

FIG. 2 is an enlarged sectional side view of a portion of the fluid collection, mixing and distribution system of the front wall shown in FIG. 1;

FIG. 2A is a sectional plan detail view along line 2A-2A of FIG. 2;

FIG. 3 is a sectional front detail view of an embodiment of the invention also shown in FIG. 2;

FIG. 3A is a sectional side detail view taken along line 3A- 3A of FIG. 3; I

FIG. 4 is a sectional front detail view of an alternate embodiment of the invention;

FIG. 4A is a sectional side detail view taken along line A- 4A of FIG. 4;

FIG. 5 is a sectional front detail view of a further alternate embodiment of the invention.

FIG. 5A is a sectional side detail view taken along line 5A 5A of FIG. 5;

FIG. 5B is a sectional plan view taken along line 58-58 of FIG. 5;

FIG. 6 is still a further alternate embodiment of the invention;

FIG. 6A is a detail view of the juncture of the superposed lugs shown in FIG. 6;

FIG. 6B is a sectional plan detail view taken along line 68- 6B of FIG. 6A;

FIG. 6C is a detail view of the juncture of the superposed lugs taken along line 6C--6C of FIG. 68;

FIG. 7 is a sectional front detail view of still another embodiment of the invention;

FIG. 7A is a sectional side detail view taken along line 7A- 7A of FIG. 7.

DESCRIPTION OF THE PREFERRED EMBODIMENTS v In the drawings, the invention has been illustrated as embodied in a top-supported forced flow one-through steam generator intended for central station use.-

The main portions of the unit as illustrated in FIG. 1, in-.

clude an upright furnace chamber 10 of substantially rectangular horizontal cross-section defined by front wall 11, rear wall 13, side walls 14, a roof I6 and a hopper 17 and having a gas outlet 18 at its upper end opening to a horizontally extending gas passage 19 of rectangular vertical cross-section form ed by a floor2l and extensions of the furnace roof 16 and side walls 14. Gas passage 19 communicates at its rear end with the upper end of an upright gas passage 22 of rectangular horizontal cross-secton fonned by a front wall 23, a rear wall 24, side walls 26, and an extension of the roof of the gas passage 19.

The fuel firing section comprises vertically spaced rows of burners 27 disposed on opposite walls 11 and 13 at the lower portion of the furnace chamber 10.

The gas passage 19 is occupied by a secondary superheater 28 and a reheater 29 arranged in series with respect to gas flow while gas passage 22 is occupied in the direction of gas flow by a primary superheater 33 and an economizer 34.

In the normal operation of the fluid heating unit, combustion air and fuel are supplied to the burners 37 and the fuel is burned in the lower portion of the furnace. Heating gases flow upwardly through chamber 10 to the furnace outlet, thence to gas passage 19 and then pass successively overand between the tubes of secondary superheater 28 and reheater 29 in gas passage 19 and over and between the tubes of primary superheater 33 and economizer 34 in gas passage 22, and discharge to another heat trap, not shown,- before entering to the stack, now shown. It will be understood that in accordance with well-known practice, each of the superheater and reheater sections extend across the full width of its corresponding gas passage and is formed for serial flow of steam by multiple looped tubes.

The vapor generating system is top supported by structural members including upright members and cross beams 90,

from which hangers 95, of which only a few are illustrated support all walls and convection surfaces.

Feedwater at high pressure is supplied by a feed pump, not shown, to economizer inlet header 25, then passes through economizer 34 to outlet header 30, from which it flows through a downcomer 35'for flow to the furnace boundary wall fluid heating circuitry.

Each of the upright boundary walls of the furnace and gas passages 19 and 22 are of gas tight construction and include parallel tubes; front wall 23 having tubes 71 extending between inlet and outlet headers 72 and 73, rear wall 24, having tubes 74 extending between inlet and outlet headers 76 and 77, each side wall 26 having tubes 78 extending between inlet headers 79 and 83 and outlet headers 81 and 84. Floor 21 is formed by a row of tubes 86 having their inlet ends connected to header 52 and their outlet ends to header 73, with header 73 being connected for fluid flow to header 88 by a row of screen tubes 89. Headers 72, 76, 79 and 83 are connected for parallel supply of fluid from a conduit 69, while headers 77, 81, 84 and 88 are arranged for discharge to another collector header 91, from which fluid passes to the primary superheater via conduit 92 and inlet header 52. From primary superheater 33, the partly superheated vapor passes through an outlet header 55 and in through inlet header 57 to the secondary superheater 28, within which the vapor receives its final superheating before passing through an outlet header 59 to a high pressure turbine, not shown. Partially expanded steam from the high pressure turbine passes through reheater 29, and from thence to the reheat pressure turbine wherein final expansion takes place.

Each of the upright boundary walls of fumace is formed by upwardly extending parallel tubes arranged to provide two upflow fluid heating passes and having their intertube spacing closed throughout most of their length by metallic webs welded to adjacent tubes to provide a gas-tight construction. The first heating pass comprises the first group of tubes and forms the lower portion of each furnace wall and the second fluid heating pass comprises the second group of tubes and forms the'upper portion of each furnace wall. Special header provisions are made for mixing the heat absorbing medium intermediate its flow from one pass to another, the mixing system from each of the fluid heating passes being specifically for the purpose of keeping the wall tube temperature differentials across the width of the furnace wall panel to a minimum. With differences in furnace cleanliness as well as in the flow rates in the multiple parallel fluid flow paths it is possible to develop temperature differences between adjacent tubes of amagnitude sufficient to induce high stresses in the tubes and in the metallic webs therebetween. By limiting the total absorption in a furnace heating pass, the degree of thermal imbalancewithin the tubes comprising the parallel flow paths is also limited. Accordingly, the boundary wall of the furnace 'is designed so that the temperature at a particular level of furnace height or elevation differs by no more than a predetermined value fromthe calculated average fluid temperature of all furnace wall tubes at that level; thus calculated maximum temperature differential between adjacent tubes is below the predetermined critical limit to minimize fluid flow imbalances; and so that the tubes of each fluid heating pass are sufficient in flow area to provide an adequate circulation rate. Further, all heated tubes of the furnace boundary walls are arranged for upflow of fluid, since flow stability within heating passes having their tubes so arranged is markedly improved over that condition where flow circuitry has heated downflow as well as upflow tubes. In other words, flow imbalances for the same average and unbalanced heat absorption conditions are considerably less severe with all upflow tubes than with both upflow and downfiow circuitry within a heat absorbing zone.

The front wall 11 comprises first pass upflow tubes 37A, 37A and second pass upflow tubes 37B, 378. Rear wall 13 includes first pass upflow 38A, 38A and second pass upflow tubes 38B, 38B with the second pass tubes forming a screen extending through gas passage 19 and the remainder forming a nose arch 41. Each side wall 14 includes first pass upflow tubes 39A, 39A and second pass upflow tubes 39B, 398'.

First pass upflow 37A, 37A, 38A, 38A, 39A, 39A of the front, rear and side walls of furnace 10 have their inlet ends connected to inlet headers 44 associated with the correspond ing walls and their upper ends connected to intermediate outlet headers 49 associated with the corresponding walls. lnlet headers 44 are supplied with fluid from conduit 35. Fluid passing through first pass upflow tubes 37A, 37A, 38A, 38A, 39A, 39A is collected in intermediate or first pass outlet headers 49 and then passed through conduit SIto second pass inlet headers 52 arranged to supply fluid to second pass upflow tubes 37B, 37B, 38B, 38B, 39B, 398. The second pass upflow tubes extend from inlet headers 52, associated with the corresponding walls, to the top of the furnace, tubes 37B, 37B having their discharge ends connected to second pass outlet header 53, some of the tubes 38B, 388' having their discharge ends connected to screen tube inlet header 73 and the remainder to screen tube outlet header 88, and tubes 39B, 39B having their discharge ends connected to headers 63. Thefluid discharges from headers 53 and 63 flow through the tubes forming the roof 16 and thereafter into the conduit 69.

From the above description it is evident that tubes 37A, 37A, 38A, 38A, 39A, 39A constitute the first fluid heating pass of the furnace, and tubes 37B, 37B, 38B, 38B, 39B, 398 the second fluid heating pass. The tubes of the first heating pass are substantially coextensive within each respective wall and have their intertube spaces closed by metallic-webs 103, weld-united to the tubes along substantially their entire parallel lengths. Tubes of the second fluid heating pass, with the exception of screen tubes, have their intertube spaces closed by metallic webs 104, weld-united to the tubes along substantially their entire lengths. Tubes of the second fluid heating pass of each upright wall, except for the rear wall of the furnace, are coplanar along almost their entire length within their respective walls and are also coplanar with the tubes of the associated first fluid heating pass of the corresponding wall.

Since the construction and arrangement of the fluid collection, mixing and distribution systems and their associated tubes are substantially the same in all walls, it will suffice to describe the front wall system fluid heating passes.

Referring to FIG. 2 there is shown a sectional side view of a portion of the fluid collection, mixing and distribution system of the front wall wherein the discharge portion of the first pass tubes 37A are bent outwardly from the plane of the wall 1 1 at the first level 101 and then extend horizontally and downwardly for radial connection to first pass outlet header.

49. The discharge portions of the first pass tubes 37A are bent outwardly from the plane of the wall 11 at about the second level 102A and extend horizontally and downwardly for radial connection to first pass outlet header 49. The fluids discharged from the first heating pass tubes 37A, 37A, also referred to as the first group of tubes, are collected and mixed in the header 49 to neutralize the difi'erences in amount of heat picked up before being passed to the second pass inlet header 52 via exterior conduits 51 for uniform distribution to the parallel flow tubes 37B, 378', also referred to as the second group of tubes, and comprising the. front wall second fluid heating pass. Inlet portions of the second pass tubes 37B extend from inlet header 52 radially inward and then bend upwardly to enter the front wall 11 at about the first level 101A from whence they extend upwardly in the plane of the wall and in contiguous relation with the adjacent portions of the first pass tubes 37A. lnlet portions of the second pass tubes 37B extend radially outward, vertically, then horizontally and then bend upwardly to enter the front wall 11 at the second level 102 from whence they extend upwardly and in contiguous relation with the second pass tubes 378 which entered the plane of the wall at the about level 101A. Metallic webs 103 close the spaces between the first pass tubes 37A, 37A up to the first level 101, while metallic webs 104 close the spaces between the second pass tubes 37B, 378' above the second level 102. The wall intertube spaces intennediate the first and second levels are partially closed by metallic fin plates 105 except at the points where tubes 37A, 37A, 37B, 37B bend out of the plane of the wall. Closure is provided at these points by metallic scalloped plates 106 suitably shaped to fit the bent tube portions. Metallic supported lugs 108 are welded to the interlaced portions of the first heating pass tubes 37A which are part of the first group of tubes, and the support lugs 107 are welded to the interlaced portions of the second heating pass tubes 37B which are part of the second group of tubes. An elongated flat metal plate 109 lies contiguous to the wall 11 and extends across the width of the wall and is interposed between and slidably engaged with the support and supported lugs 107 and 108, respectively, to transmit the load of the first group of tubes to the second group of tubes. A wall box 99, formed by a welded metal casing 111 and including a suitable refractory material 112, provides a gas-tight seal for the detached tube area existing between the levels 101 and 102.

Thusat the locations where mixing of the fluids occurs as they flow from one furnace fluid heating pass to another, the interlaced tube portions of the first and second heating passes as well as the points where the tubes of both these heating passes bend out of the plane of the wall, are detached from one another with the first pass heating tubes forming the lower portion of the wall and being connected for support by the second pass heating tubes through a slidable support arrangement capable of absorbing the expansion and contraction of the tube wall during the heating and cooling of the unit.

Referring to FIG. 2A there is shown a sectional plan detail view of some of the interlaced tube portions of front wall 11 depicting first and second pass heating tubes 37A and 373 with their intertube spacing partially closed by the fin plates 105 and backed by a suitable refractory 112 to form a gastight seal.

Referring to FIGS. 3 and 3A there are shown sectional front and'side detail views, respectively, taken at the interlaced tube portions and depicting an embodiment of the invention including a section of the elongated metal plate 109 lying contiguous to a section of the interlaced first and second pass tube portions 37A and 37B. The support lugs 107 are formed with a base portion 107A and a finger portion 1073 and have the base portion welded to the interlaced portion of the second pass tubes 37B. The supported lugs 108 are formed with a base portion 108A and a finger portion 1088 and have the base portion welded to the interlaced portion of the first pass tubes 37A. Top and bottom sections of metal plate 109 are interposed between the support lugs and slidably engaged therewith. The intertube spacing between the interlaced tube portions is partially closed by the fin plates 105 and the spacing between the levels 101 and 101A is partially closed by the scalloped plates 106. The intertube spaces below the level 101 where the tubes 37A leave the plane of the wall are closed by metallic webs 103. l

The metallic fin plates 105 are arranged in rows disposed on opposite sides of the interlaced tube portions and welded thereto. One typical arrangement calls for two rows of plates spanning the intertube spacing, each row being associated with one of two adjacent tubes and including fin plates 105 measuring 1 to 3 inches in length and spanning nearly one-half the width of the intertube spacing, the fin plates being serially spaced one-sixteenth to one-fourth inches and the adjacent rows being laterally spaced one-sixteenth to one-fourth inches. Another arrangement has the fin plates spanning nearly the entire width of the intertubespacing and forming a single row welded to only one of two adjacent tubes. Still another arrangement has fin plates spanning nearly the entire width of the intertube spacing and forming two intermeshed rows whereby alternate fins are welded to the other of two adjacent tubes. These latter two arrangements which are not shown in the drawings are also serially and laterally spaced in the range of one-sixteenth to one-fourth inches. The scalloped plates 106 consist of two plates having adjacent sides shaped to fit the contour of the tubes as they bend out of the plane of the wall and having their opposite sides welded to adjacent interlaced tube portions.

The weight-load of the first pass tubes 37A is transmitted to the first pass tubes 37A through the metallic webs 103. The combined weight-load of the lower portion of the furnace as represented by tubes 37A and 37A is transmitted through the supported lugs 108, associated with tubes 37A to the elongated metal plate 109 which in turn transmits the lower furnace portion weight-load to the support lugs 107 associated with the second pass tubes 373, the latter together with the second pass tubes 378' form the upper portion of the furnace. The weight-load transmitted through the lugs-107 is partially taken-up by the tubes 378 with the rest being passed to the tubes 378' through the metallic webs 104. The tubes 37B and 37B attach to a fluid discharge header 53 which is connected by hangers for support by upright members 85 and cross beams-90. The wall arrangement thus provided is capable of absorbing the expansion and contraction of the tube sections at the interlaced portion by leaving each of the support lugs 107 and the corresponding supported lug 108 free to move independently of one another along the bar 109.

Referring to FIGS. 4 and 4A there are shown sectional front and side detail views, respectively, taken at the interlaced tube portions and depicting an alternate embodiment of the invention including a plurality of plates 110 lying contiguous to a section of the interlaced first and second pass tube portions 37A and 37B. Each of the plates 110 being of rectangular shape and sized to cover a section of a corresponding interlaced portion of second pass tube 373 and to overlap sections of the oppositely adjacent interlaced portions of first pass tubes 37A. Each upright side of the plate 110 is welded to the corresponding overlapped section of first pass tube 37A. The support lugs 107 are welded to the second pass tubes 37B and are arranged to slidably engage a bottom section of a corresponding plate 110. The intertube spacing between the interlaced tube portions is partially closed by the fin plates which are fully set forth in the description of FIGS. 3 and 3A.

The weight-load of the lower portion of the furnace is transmitted through the individual plates associated with the first pass tubes 37A to the support lugs 107 associated with the second pass tubes 37B, these'latter tubes are part of the upper portion of the furnace wall which is connected for support to the structural steel supporting the vapor generating system. The wall arrangement thus provided allows each of the plates 110 and the corresponding support lug 107 to move independently of one another.

Referring to FIGS. 5, 5A and 58 there are shown sectional front, sideand plan detail views, r'espectively,taken at the interlaced tube portions and depicting an alternate embodiment of the'invention including tube-shaped support lugs 121 and tube-shaped supported lugs 122. Each support lug 121 is welded along its axial length to a section of a corresponding interlaced portion of a second pass tube 373 and each supported lug 122 is welded along its axial length to a section of a corresponding interlaced portion of a first pass tube 37A. There are two support lugs associated with each tube 378 and two supported lugs associated with tube 37A. The support and supported lugs extend outwardly of the plane of the wall in a radial direction so as to overlap the adjoining intertube spacings and each supported lug 122 is superposed to the adjacent support lug 121 and is axially aligned therewith to form a common bore therethrough. A pin 113 is slidably fitted through the bore and extends slightly beyond the ends of the bore. The upper end of pin 113 is welded to a portion of the top cross-sectional surface of supported lug 122. The support lug 121 remains free to move with respect to the pin 113. The intertube spacing between the interlaced tube portions is partially closed by the fin plates 105 which are fully set forth in the description of FIGS. 3 and 3A.

The weight load of the lower portion of the furnace is transmitted through the support lugs 122 associated with the first pass tubes 37A to the support lugs 121 associated with the second pass tubes 373, these latter tubes are part of the upper portion of the furnace wall which is connected for support to the structural steel supporting the vapor generating system. The wall arrangement thus provided allows each of the support lugs 121 and the corresponding support lug 122 with its attached pin 1 13 to move independently of one another.

Referring to FIGS. 6, 6A, 6B and 6C there are shown sectional front, side and plan detail views, respectively, taken at the interlaced tube portions and depicting a further alternate embodiment of the invention including support lugs 114 and supported lugs 115 in the form of elongated fixtures extending parallel to and intersecting a plane common to the longitudinal axes of the interlaced tube portions. Each support lug 114 is welded along its axial length to a section of a corresponding interlaced portion of a second pass tube 37B and eachsupported lug 115 is welded along its axial length to a section of a corresponding interlaced portion of a first pass tube 37A, there are two support lugs associated with each tube-37B and two supported lugs associated with each tube 37A. Each supported lug 115 is superposed to the adjacent support lug 114 with the abutting ends being slidably engaged to one another. The abutting end of each support lug 115 is formed with a grooved portion 115A sized to slidably accommodate a tongue portion 114A formed on the abutting end of each support lug 114. The intertube spacing between the interlaced tube portions is partially closed by the fin plates 105 which are fully set forth in the description of FIGS. 3 and 3A.

The weight of the lower portion of the furnace is trans mitted through the supported lugs 1 associated with the first pass tubes 37A to the support lugs 114 associated with the second pass tubes 378, these latter tubes are part of the upper portion of the furnace wall which is connected for support to the structural steel supporting the vapor generating system. The wall arrangement thus provided allows the support lug I15 and the corresponding support lug 114 to move independently of one another.

Referring to FIGS. 7 and 7A there are shown sectional front and side detail views, respectively, taken at the interlaced tube portions and depicting still another embodiment of the invention including the discharge portions of first pass tubes 37A which are bent outwardly from the plane of the wall 11 at the first level 101 for connection to the first pass outlet header 49 (not shown). The discharge portions of the first pass tubes 37A are bent outwardly from the plane of the wall 1 1 at about the second level 102A for connection to first pass outlet header 49 (not shown). The inlet portions of the second pass tubes 37B extend from the second pass inlet header 52 (not shown) and bend upwardly to enter the front wall 1 1 at about the first level 101A from whence they extend upwardly in the plane of the wall and in contiguous relation with adjacent portions of the first pass tubes 37A. Inlet portions of the second pass tubes 37B extend from the second pass inlet header 52 (not shown) and bend upwardly to enter the front wall 11 at the second level 102 from whence they extend upwardly and in contiguous relation with the second pass tubes 378 which entered the plane of the wall at the about level 101A. The supported lugs 108 are welded to the first pass tubes 37A at a location subjacent to the level 101 and to the interlaced portions of the first pass tubes 37A at a location subjacent to the about level 102A. The support lugs 107 are welded to the interlaced portions of the second pass tubes 378 at a location superjacent to the about level 101A and to the second pass tubes 3713' at a location superjacent to the level 102. Elongated flat metal plates 116A, B, C and D are substantially equal in size and disposed in contiguous relationship to a section of wall 11 and have their longitudinal extent lying across the width of the wall. A top section of plate 116A is slidably engaged with the supported lugs 108 attached to the tubes 37A. A bottom section of plate [163 is slidably engaged with the support lugs 107 attached to the tubes 378. The plates 116A and 1168 are interconnected by support bars 117 which have their respective end portions extending across the width of these plates and are welded thereto. A top section of plate 1 16C is slidably engaged with the support lugs 108 attached to the tubes 37A. A bottom section of plate 116D is slidably engaged with the support lugs 107 attached to the tubes 378'. The plates 116C and 116D are interconnected by support bars 1 17 in like manner to the interconnection of plates 116A and 1168. The intertube spacing between the interlaced tube portions is partially closed by the fin plates and the spacing between the levels 101 and 101A and between the levels 102 and 102Ais partially closed by the scalloped plates 106. The intertube spaces below the level 101 where the tubes 37A leave the plane of the wall are closed by metallic webs 103 and the intertube spaces above the level 102 where the tubes 37B enter the plane of the wall are closed by metallic webs 104. The aforementioned plates are fully set forth in the description of FIGS. 3 and 3A.

The weight-load of the first pass tubes 37A is transmitted through the support lugs 108, associated with the tubes 37A, to the plate 116A which is in tumsupportingly connected to the plate 116B by way of the support bars 117 associated therewith. The plate116B transmits this weightload to the tubes 378 through the support lugs 107 associated with the tubes 378. The weight-load of the tubes 37A is transmitted through the support lugs 108, associated with the tubes 37A, to the plate 116C which is in turn supportingly connected to the plate 116D by wayof the support bars 117 associated therewith. The plate 116D transmits this weight-load to the tubes 378' through the support lugs 107 associated with the tubes 378. The tubes 37B and 378' form the upper portion of the furnace wall which is connected for support to the structural steel supporting the vapor generating system. The wall arrangement thus provided allows each of the support lugs 107 and corresponding support lugs 108 free to move independently of one another. I

What is claimed is:

1. In a forced circulation fluid heating unit, upright walls forming a furnace chamber, at least one of the walls including a first group of upwardly extending laterally spaced fluid heating tubes rigidly united throughout most of their lengths and forming a lower portion of said one wall, a second group of upwardly extending laterally spaced fluid heating tubes rigidly united throughout most of their lengths and forming an upper portion of said one wall, means for supplying fluid to the tubes of the first group, header means communicating with and receiving and mixing fluids flowing from the tubes of the first group and distributing mixed fluids to tubes of the second group, some of the tubes of the first and second groups being bent out of the plane of the wall at first and'second levels, respectively for connection to the header means, and interlaced with each other in the plane of the wall between the first and second levels, said first level being subjacent the second level, the remainder of the tubes of the first and second tube groups being bent out of the plane of the wall at about the second and first levels, respectively, for connection to the header means, the improvement comprising means for supporting said one wall including support lugs weld united only to the interlaced portions of the second group of tubes, means for transmitting the load of the first group of tubes to the support lugs, and means for top supporting the second group of tubes, the tube portions in the plane of the wall in the vicinity of the first and second levels and the interlaced portions therebetween being detached from one another for the most pan 2. In a forced circulation fluid heating unit according to claim 1 wherein the means for transmitting the load of the first group of tubes to the support lugs includes a plurality of plates, each plate slidably engaged with at least one support lug and weld united to oppositely adjacent interlaced tube portions of the first group of tubes.

3. In a forced circulation fluid heating unit according to claim 1 wherein the means for supporting said one wall includes supported lugs weldunited only to the interlaced portions of the first group of tubes.

4. In a forced circulation fluid heating unit according to claim 3 wherein said support lugs and supported lugs are vertically spaced from one another in the plane of the wall.

5. In a forced circulation fluid heating unit according to claim 4 wherein the means for transmitting the load of the first group of tubes to the support lugs includes plate means interposed between said support lugs and supported lugs and slidably engaged therewith.

6. In a forced circulation fluid heating unit according to claim 3 wherein each of said support lugs and supported lugs extends normal to the plane of the wall and includes a base portion weld united to a corresponding tube and a finger portion spaced from said tube to provide a saddle therebetween.

7. In a forced circulation fluid heating unit according to claim 3 wherein said support lugs and supported lugs are tubeshaped.

8. In a forced circulation fluid heating unit according to claim 7 wherein each supported lug is superposed to the adjacent support lug and is axially aligned therewith to form a common bore therethrough, a pin extending through at least a major portion of the bore and weld united to said supported lug.

9. In a forced circulation fluid heating unit according to claim 3 wherein said support lugs and supported lugs are in the form of elongated fixtures extending parallel to and intersecting a plane common to the longitudinal axes of the interlaced tube portions.

10. in a forced circulation fluid heating unit according to claim 9 wherein the support lug and supported lug of adjacent tubes are superposed in end-abutting relationship.

11. In a forced circulation fluid heating unit according to claim 10 wherein one of the abutting-ends is formed with a tongue portion and the other abutting-end is formed with a grooved portion, said abutting-ends being slidably engaged with one another.

12. [n a forced circulation fluid heating unit, upright walls forming a furnace chamber, at least one of the walls including a first group of upwardly extending laterally spaced fluid heating tubes rigidly united throughout most of their lengths and forming a lower portion of said one wall, a second group of upwardly extending laterally spaced fluid heating tubes rigidly united throughout most of their lengths and forming an upper portion of said one wall, means for supplying fluid to the tubes of the first group, header means communicating with and receiving and mixing fluids flowing from the tubes of the first group and distributing mixed fluids to tubes of the second group, some of the tubes of the first and second groups being bent out of the plane of the wall at first and second levels, respectively, for connection to the header means, and interlaced with each other in the plane of the wall between the first and second levels, said first level being subjacent the second level, the remainder of the tubes of the first and second tube groups being bent out of the plane of the wall at about the second and first levels, respectively, for connection to the header means, and means for supporting said one wall including support lugs weld united only to the second group of tubes and supported lugs weld united only to the first group of tubes, means for transmitting the load of the first group of tubes to the support lugs, and means for top supporting the second group of tubes, the tube portions in the plane of the wall in the vicinity of the interlaced portions therebetween being detached from one another for the most part.

13. In a forced circulation fluid heating unit according to claim 12 wherein some of said support lugs are weld united to the interlaced portions of the second group of tubes and the remaining support lugs are weld united to the second group of tubes entering the plane of the wall at the second level, and some of said supported lugs are weld united to the first group of tubes leaving the plane of the wall at the first level and the remaining supported lugs are weld united to the interlaced portion of the first group of tubes, the means for transmitting the load of the first group of tubes to the support lugs including separate plate means slidably eggaged with the support lugs and supported lugs and means or interconnecting said plate means.

14. In a forced circulation fluid heating unit according to claim 13 wherein the means for interconnecting said plate means includes a plurality of support bars having end portions extending over at least a portion of the plate means and being weld united thereto. 

1. In a forced circulation fluid heating unit, upright walls forming a furnace chamber, at least one of the walls including a first group of upwardly extending laterally spaced fluid heating tubes rigidly united throughout most of their lengths and forming a lower portion of said one wall, a second group of upwardly extending laterally spaced fluid heating tubes rigidly united throughout most of their lengths and forming an upper portion of said one wall, means for supplying fluid to the tubes of the first group, header means communicating with and receiving and mixing fluids flowing from the tubes of the first group and distributing mixed fluids to tubes of the second group, some of the tubes of the first and second groups being bent out of the plane of the wall at first and second levels, respectively for connection to the header means, and interlaced with each other in the plane of the wall between the first and second levels, said first level being subjacent the second level, the remainder of the tubes of the first and second tube groups being bent out of the plane of the wall at about the second and first levels, respectively, for connection to the header means, the improvement comprising means for supporting said one wall including support lugs weld united only to the interlaced portions of the second group of tubes, means for transmitting the load of the first group of tubes to the support lugs, and means for top supporting the second group of tubes, the tube portions in the plane of the wall in the vicinity of the first and second levels and the interlaced portions therebetween being detached from one another for the most part.
 2. In a forced circulation fluid heating unit according to claim 1 wherein the means for transmitting the load of the first group of tubes to the support lugs includes a plurality of plates, each plate slidably engaged with at least one support lug and weld united to oppositely adjacent interlaced tube portions of the first group of tubes.
 3. In a forced circulation fluid heating unit according to claim 1 wherein the means for supporting said one wall includes supported lugs weld united only to the interlaced portions of the first group of tubes.
 4. In a forced circulation fluid heating unit according to claim 3 wherein said support lugs and supported lugs are vertically spaced from one another in the plane of the wall.
 5. In a forced circulation fluid heating unit according to claim 4 wherein the means for transmitting the load of the first group of tubes to the support lugs includes plate means interposed between said support lugs and supported lugs and slidably engaged therewith.
 6. In a forced circulation fluid heating unit according to claim 3 wherein each of said support lugs and supported lugs extends nOrmal to the plane of the wall and includes a base portion weld united to a corresponding tube and a finger portion spaced from said tube to provide a saddle therebetween.
 7. In a forced circulation fluid heating unit according to claim 3 wherein said support lugs and supported lugs are tube-shaped.
 8. In a forced circulation fluid heating unit according to claim 7 wherein each supported lug is superposed to the adjacent support lug and is axially aligned therewith to form a common bore therethrough, a pin extending through at least a major portion of the bore and weld united to said supported lug.
 9. In a forced circulation fluid heating unit according to claim 3 wherein said support lugs and supported lugs are in the form of elongated fixtures extending parallel to and intersecting a plane common to the longitudinal axes of the interlaced tube portions.
 10. In a forced circulation fluid heating unit according to claim 9 wherein the support lug and supported lug of adjacent tubes are superposed in end-abutting relationship.
 11. In a forced circulation fluid heating unit according to claim 10 wherein one of the abutting-ends is formed with a tongue portion and the other abutting-end is formed with a grooved portion, said abutting-ends being slidably engaged with one another.
 12. In a forced circulation fluid heating unit, upright walls forming a furnace chamber, at least one of the walls including a first group of upwardly extending laterally spaced fluid heating tubes rigidly united throughout most of their lengths and forming a lower portion of said one wall, a second group of upwardly extending laterally spaced fluid heating tubes rigidly united throughout most of their lengths and forming an upper portion of said one wall, means for supplying fluid to the tubes of the first group, header means communicating with and receiving and mixing fluids flowing from the tubes of the first group and distributing mixed fluids to tubes of the second group, some of the tubes of the first and second groups being bent out of the plane of the wall at first and second levels, respectively, for connection to the header means, and interlaced with each other in the plane of the wall between the first and second levels, said first level being subjacent the second level, the remainder of the tubes of the first and second tube groups being bent out of the plane of the wall at about the second and first levels, respectively, for connection to the header means, and means for supporting said one wall including support lugs weld united only to the second group of tubes and supported lugs weld united only to the first group of tubes, means for transmitting the load of the first group of tubes to the support lugs, and means for top supporting the second group of tubes, the tube portions in the plane of the wall in the vicinity of the interlaced portions therebetween being detached from one another for the most part.
 13. In a forced circulation fluid heating unit according to claim 12 wherein some of said support lugs are weld united to the interlaced portions of the second group of tubes and the remaining support lugs are weld united to the second group of tubes entering the plane of the wall at the second level, and some of said supported lugs are weld united to the first group of tubes leaving the plane of the wall at the first level and the remaining supported lugs are weld united to the interlaced portion of the first group of tubes, the means for transmitting the load of the first group of tubes to the support lugs including separate plate means slidably engaged with the support lugs and supported lugs and means for interconnecting said plate means.
 14. In a forced circulation fluid heating unit according to claim 13 wherein the means for interconnecting said plate means includes a plurality of support bars having end portions extending over at least a portion of the plate means and being weld united thereto. 